In recent years, rotary electric machines such as electric motors and electric generators have been required to be high in efficiency and small in vibration. One of methods for achieving a motor that is small in vibration is to reduce the slot opening width of an armature. If the slot opening width is reduced, salient poles of the armature are decreased, whereby vibration can be suppressed. Here, the salient pole means a magnetic projection. In the armature, teeth are formed by iron and slots are formed by gaps (nonmagnetic coils), and therefore, as seen from the inner-side surface of the armature, tooth portions having small magnetic resistance and gaps having high magnetic resistance are arranged alternately, and thus the magnetic resistance appears in a discontinuous irregular form. This irregularity becomes a cause of vibration, and it is necessary to reduce the irregularity as much as possible in order to eliminate the vibration. However, if the ends of the teeth are too close to each other, a leakage magnetic flux circulating in a stator without passing through a rotor increases, thereby output is reduced.
In order to solve such a problem, Patent Document 1 discloses a plate-shaped core sheet having a plurality of core portions and a bridging portion via which the radially inner side ends of the plurality of core portions are connected to each other. And the bridging portion has a thin portion which is thinner than the plate thickness of the core sheet, and a part corresponding to the bridging portion has a greater magnetic resistance than the other parts. Thus, a leakage magnetic flux leaking and flowing to the bridging portion during operation of a brushless motor can be reduced, and decrease in an effective magnetic flux flowing in the core portion can be suppressed.